Intra-body flow distributor for heat exchanger

ABSTRACT

A flow distributor for mounting in an inlet of a heat exchanger includes a nose cone and one or more diverting rings. The nose cone is aerodynamically shaped to divert impingent gas flow around the nose cone. A first diverting ring is spaced outwardly from the nose cone and can be oriented such that at least a portion of the gas flow diverted by the nose cone is redirected into the wake of the nose cone. A second diverting ring can be spaced outwardly from the first diverting ring and can be oriented to divert gas flow impingent thereon. Struts connect the nose cone and one or more rings. Refractory on the wall of the inlet is shaped to reduce the recirculation at the outer perimeter thereof. The flow distributor is installed in the inlet with refractory to achieve substantially equal flow across the tube sheet of the heat exchanger.

FIELD OF THE INVENTION

The subject matter of the present disclosure relates generally to adevice for distributing gas flow in a pipe that feeds the gas into aheat exchanger. More particularly, the subject matter of the presentdisclosure relates to a flow distributor mounted in an inlet section ofa transfer line heat exchanger for evenly distributing gas flow to atube sheet of the heat exchanger.

BACKGROUND OF THE INVENTION

Thermal cracking of hydrocarbons is a large-scale process for theproduction of light olefins, such as ethylene and propylene, which aremajor building blocks of the petrochemical industry. Referring to FIG.1, a portion of a thermal cracking process is schematically illustrated.Feedstock, such as naphtha, methane, ethane, propane, or butane, iscracked in a pyrolysis or cracking furnace (not shown) to generate lighthydrocarbons. The process gas leaves the furnace at temperatures rangingfrom 750 to 900° C. (1400 to 1650° F.) and at pressures between 0.5 to1.0 bar (7 to 15 psig). The products in the process gas leaving thefurnace are not stable at the high temperature at the outlet of thefurnace. To avoid overreactions and loss of light olefins, the processgas is rapidly cooled after leaving the furnace in a number of quenchingstages, which quickly stop the chemical reactions of the process gas.

An initial quenching stage uses a transfer line heat exchanger 30 knownin the art. The transfer line heat exchanger 30 is a tube and shell typeheat exchanger that is cooled by feed water steam as an intermediateheat carrier. Piping 20 connects the source of the process gas (e.g.,the furnace) to the transfer line heat exchanger 30. Typically, thetransfer line heat exchanger 30 is much larger in diameter than thepiping 20 used to convey the process gas so that an inlet section 22 istypically used to expand the piping 20 to fit the larger diameter of thetransfer line heat exchanger 30.

The transfer line heat exchanger 30 includes a shell 32, a plurality ofheat transfer tubes 34, an inlet tube sheet 36, and an outlet tube sheet38. An inlet 40 and an outlet 42 for feed water connect to the shell 32.The heat exchanger 30 may contain as many as 1500 to 2000 transfer tubes34 through which the process gas flows from an inlet section 22 to anoutlet section 24. The transfer tubes 34 are connected to holes in thetube sheets 36 and 38. Tie rods and baffle plates within the shell 32are used with the bundle of tubes 34. As the tubes 34 carry the gasthrough the shell 32 of the heat exchanger 30, the tubes 34 aresurrounded by feed water steam that flows through the shell 32 of theheat exchanger 30 for cooling the process gas. The discharge section 24connects to additional piping 26 of the process system, where theprocess gas is taken to for continued processing, such as further quenchstages to cool the gas. When quenching the process gas during use, thestream of process gas after leaving the furnace of the industrialcracker may be cooled within the heat exchanger 30 from 850° C. or more,down to 400° C. or less.

Referring to FIG. 2, the inlet section 22 and the inlet tube sheet 36 ofthe transfer line heat exchanger are schematically shown. The inletsection 22 and tube sheet 36 are symmetric about a central axis C sothat only a portion of the inlet section 22 and tube sheet 36 is shownfor convenience. The inlet section 22 is typically lined with refractory40 for thermally insulating the inlet section 22. Streamlines Gschematically show the laminar flow of the process gas as it travelsfrom the furnace piping 20, to the inlet section 22, through the holesin the tube sheet 36, and into the transfer tubes 34. As noted above,the tube sheet 36 typically has a number of transfer tubes connected toholes 37 in the tube sheet 36. Only a few tubes 34 are illustrated forconvenience.

As is known in the art of chemical processing, the transfer line heatexchanger 30 such as described herein can suffer from a number ofproblems. For example, problems can occur at the inlet tube sheet 36 ofthe exchanger 30. In many applications, for example, a recirculationzone can occur in the inlet section 22 near the face F of the inlet tubesheet 36. The recirculation zone is schematically shown in FIG. 2 nearthe periphery of the inlet tube sheet 36. The geometry of the inletsection 22 along with the flow rate of the process gas creates therecirculation zone in the inlet section 22. The formation of therecirculation zone thereby increases the peak velocity at the tube sheet38, which can be as great as 1880 in/sec, for example. Ideally, if theformation of the recirculation zone did not occur, the process gas wouldbe more uniformly distributed at the face of the tube sheet 36, and theaverage velocity would be approximately 566 in/sec, for example.

Due to the recirculation, the process gas may be poorly distributed atthe face of the tube sheet, and the velocity of the process gas isgreater than ideally desired. Under these conditions, the heat transferfilm coefficients on the face F (i.e., the process gas side) of the tubesheet 36 will be higher than ideal, and the associated temperatures willbe higher than if the flow of the process gas were more evenlydistributed. In addition, recirculation can cause fouling on certainportions of the tube sheet 38, for example the outer edge, so that thechances of plugging of certain tubes 34 are increased. For example, theformation of carbonaceous deposits can accumulate near the periphery ofthe tube sheet 36, diminishing the ability of the process gas to passthrough the outer tubes 34. Such fouling conditions decrease theefficiency of the system.

If a group of tubes 34 becomes plugged from the recirculating gas, thenthe peak velocity near the open portion of the tube sheet 36 willfurther increase, creating jetting conditions or a jetting zone in thepiping 20 and inlet section 22. The high velocity gas streams in thejetting zone can produce film boiling on the tube sheet 36. As is knownin the art, film boiling can cause the welded joint of the tubes 34 tothe sheet to fail and can exacerbate corrosion at the welded joint. Inaddition, erosion of the tube sheet 36 can occur if there are particlesin the process gas, and such erosion can be further compounded ifjetting conditions are produced.

To reduce the problem of fouling, periodic removal of the foulingdeposits may be necessary. Typically, the transfer line heat exchanger30 must be put out of service to remove the fouling. In the art,coatings may also be used to reduce the potential for fouling.Unfortunately, the intense heat of the process gas in the inlet section22 can quickly destroy any such coatings. To solve problems related torecirculation and jetting conditions, it is known in the art to form therefractory 40 in the inlet section 22 in a shape that can reduce therecirculation of the process gas near the edge of the tube sheet 36. Forexample, the refractory 40 may be given a “bell” or “trumpet” shape fromthe piping 20 to the face F of the tube sheet 36. Other solutions in theprior art include inserting a piece of equipment to breakup the gas flowin the inlet section 22. Because the heat of the process gas is sointense, the equipment used to break up the flow can be quicklydestroyed, which can lead to additional problems. To prevent erosion,another device known in the art, called an “Erosion Protection Shield”manufactured by Borsig Gmbh, is placed in the inlet section.

The subject matter of the present disclosure is directed to overcoming,or at least reducing the effects of, one or more of the problems setforth above.

SUMMARY OF THE DISCLOSURE

An intra-body flow distributor for distributing gas flow in an inletinto a heat exchanger is disclosed. The distributor includes a nose coneand one or more diverting rings. The nose cone has a leading portion anda trailing portion and is aerodynamically shaped to divert impingent gasflow around the nose cone. A first diverting ring is spaced outwardlyfrom the nose cone. The first diverter ring can be oriented such thatgas flow diverted by the nose cone is redirected into the shadow of thetrailing portion of the nose cone. A second diverting ring can be spacedoutwardly from the first diverting ring and can be oriented to redirectgas flow both inwardly and outwardly of the second ring. If necessary,additional rings can then be spaced outwardly from the second divertingring and can be oriented to redirect gas flow both inwardly andoutwardly of the additional ring. A plurality of first struts connectsthe first diverting ring to the nose cone, and a plurality of secondstruts connects the second diverting ring to the first diverting ring.The distributor preferably mounts in the inlet section of the transferline hear exchanger using a plurality of rods and anchors. Smooth endsof the rods preferably fit loosely into holes in the nose cone. Theanchors are preferably cast in refractory of the inlet section. Threadedends of the rods then preferably thread into the threaded openings inthe anchors to mount the distributor in the inlet section.

A method for improving the distribution of gas flow in an existingprocess heat exchanger system is disclosed. The existing process heatexchanger system includes gas flow piping and a heat exchanger inputsection. The method includes modeling the gas flow characteristics ofthe existing process heat exchanger system and thereby optimizing theshape of the refractory in the heat exchanger input section based on thegas flow characteristics. Next, the size and orientation of a flowdistributor having a nose cone and one or more diverting rings isoptimized to substantially evenly distribute the process gas at the tubesheet of the existing process heat exchanger system. The size andorientation of the nose cone is optimized to distribute any centrallylocated jet of gas. To optimize the nose cone, a position along acentral axis of the input section, a diameter, an axial expanse, or asurface curvature of the nose cone can be iteratively determined. Thesize and orientation within the input section of a first diverter ringcan be optimized to divert at least a portion of the gas flowdistributed by the nose cone into the shadow of the nose cone. Tooptimize the first diverter ring, a radius, a width, a relativeseparation from the nose cone, or an angular orientation of the firstdiverter ring can be iteratively determined. The size and orientationwithin the input section of a second diverter ring can be optimized toredirect gas flow toward and away from the second diverter ring. Usingmore than one diverter ring within the input section can be based on thesize of the input section or the characteristics of the gas flow. Anassembly is then fabricated that includes the nose cone and diverterring(s). The assembly is installed in the input section of the existingprocess heat exchanger system for substantially evenly distributing theprocess gas.

The foregoing summary is not intended to summarize each potentialembodiment or every aspect of the subject matter of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, preferred embodiments, and other aspects of thesubject matter of the present disclosure will be best understood withreference to a detailed description of specific embodiments, whichfollows, when read in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a portion of a process system having a transfer lineheat exchanger known in the art is schematically illustrated.

FIG. 2 schematically illustrates an inlet section and tube sheet of theprocess system of FIG. 1.

FIG. 3 schematically illustrates an inlet section and tube sheet of aprocess system having refractory and a flow distributor according tocertain teachings of the present disclosure.

FIGS. 4A-B illustrate side and front views of an embodiment of a flowdistributor according to certain teachings of the present disclosure.

FIG. 5 illustrates a front view of the flow distributor of FIGS. 4A-Bmounted in refractory.

FIGS. 6A-B illustrate side and cross-sectional views of a nose cone ofthe flow distributor of FIG. 5.

FIG. 7 illustrates an isolated view of a mounting rod of FIG. 5.

FIG. 8 illustrates a cross-sectional view of an anchor of FIG. 5.

While the disclosed flow distributor is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. The figures and written description are not intended to limitthe scope of the inventive concepts in any manner. Rather, the figuresand written description are provided to illustrate the inventiveconcepts to a person skilled in the art by reference to particularembodiments, as required by 35 U.S.C. § 112.

DETAILED DESCRIPTION

Referring to FIG. 3, a flow distributor 100 according to certainteachings of the present disclosure is schematically illustrated. Theflow distributor 100 is installed in an inlet section 22 connected to atransfer line heat exchanger similar to that described previously foruse in quenching stages of a thermal cracking process. Although thepresent embodiment of the flow distributor 100 is discussed for use insuch a thermal cracking process in the present disclosure, one ofordinary skill in the art will appreciate that teachings of the presentdisclosure can be used for a number of applications having flow of afluid.

The flow distributor 100 distributes the process gas from the furnacepiping 20 and inlet section 22 into the transfer line heat exchanger ofa process system. As noted above, the transfer line heat exchanger (notshown) includes a tube sheet 36 having a plurality of holes 37 forpassage of the process gas into transfer tubes 34 of the heat exchanger.Because the inlet section 22 and tube sheet 36 are symmetric about acentral axis C, only a portion of the inlet section 22 and tube sheet 36is shown in FIG. 3 for convenience. Streamlines G schematically showlaminar flow of the process gas as it travels from the furnace piping20, to the inlet section 22, and to the tube sheet 36 having thetransfer tubes 34. As noted above, the tube sheet 36 may have a largenumber of tubes 34 attached to the holes in the tube sheet 36, and onlya few are schematically shown for simplicity.

The inside wall 23 of the inlet section 22 preferably has refractory 50formed thereon. The refractory 50 is typically composed of a hightemperature insulating and castable material that is cast onto theinside wall 23 of the inlet section 22 using techniques known in theart. Preferably, the refractory 50 on the wall 23 is shaped to reducethe recirculation at the outer perimeters of the inlet section 22 andtube sheet 36 as much as possible. Suitable teachings for optimizing theshape of the refractory 50 are provided below.

The flow distributor 100 mounts in the inlet section 22 of the gas flowpiping to the heat exchanger 30. Details of a preferred technique formounting the flow distributor 100 in the refractory 50 formed in theinlet section 22 are provided below with reference to FIGS. 5-8. Tosurvive the hot gas and flow conditions present in the inlet section 22,the flow distributor 100 is preferably sand cast from a high temperaturealloy, such as 800-HT. Furthermore, the surfaces of the flow distributor100 are preferably smooth to a finish within ASTM A802 Grade A2 (nobake) tolerances.

The flow distributor 100 has optimized or iteratively determinedgeometries so that it will achieve substantially equal distribution ofprocess gas across the face F of the tube sheet 36 when installed withinthe inlet section 22. In other words, the flow distributor 100preferably orients the gas so that the gas impacts the tube sheet 36with a substantially even distribution. In addition, the flowdistributor 100 preferably orients the gas to achieve a substantiallyeven temperature gradient across the face F of the tube sheet 36.

In general, the inlet section 22 to the transfer line heat exchanger fora particular implementation may have an axial expanse D₁ of about 5 to500-inches from the furnace piping 20 to the inlet tube sheet 36. Therefractory 50 may have a radial dimension R₂ of about 5 to 500-inchesadjacent the tube sheet 36. The flow distributor 100 may have an axialexpanse D₂ of about 2 to 200-inches and may be distanced an axialexpanse D₃ from the tube sheet 36 by about 1 to 20-inches. In addition,the flow distributor 100 may have a radial dimension R₃ of about 5 to500-inches. As best described below, the various dimensions and rangesset forth above depend on a number of factors.

As only schematically shown in FIG. 3, the flow distributor 100 includesa nose cone 110 and one or more diverting rings. In the presentembodiment, the flow distributor 100 has a first diverting ring 120 anda second diverting ring 130. As will be evident with the benefit of thepresent disclosure, however, only one diverting ring or a plurality ofdiverting rings may be used on the flow distributor 100 depending on theparticular implementation. The nose cone 110 directs flow of the processgas away from the central axis C of the inlet section 22 and the tubesheet 36 in a manner that provides substantially equal flowsymmetrically around the inlet section 22. The diverting rings 120, 130direct the gas flow both inwardly and outwardly of the ring. In thepresent embodiment, the first diverting ring 120 is shown angled andsized to direct at least a portion of the diverted gas flow from thenose cone 110 back to the wake or low pressure area of the nose cone 110along the central axis C of the inlet section 22. The second divertingring 130 is shown angled and sized to direct the gas flow both inwardlyand outwardly of the second ring 130. The number of diverter rings andthe orientation and size of the various components are selected for aparticular implementation, according to teachings of the presentdisclosure. Then, the flow distributor 100 can substantially evenlydistribute gas across the face F of the tube sheet 36. As depicted bythe streamlines G, the flow distributor 100 can thereby reduce oreliminate the recirculation zones in the inlet section 22 describedabove.

Referring now to FIGS. 4A-B, a detailed embodiment of a flow distributor100 is illustrated in a front and a side view. As best shown in thefront view of FIG. 4A, the flow distributor 100 includes a firstdiverting ring 120 spaced outwardly from a nose cone 110 and includes asecond diverting ring 130 spaced outwardly from the first diverting ring120, although more or less diverting rings may be used for a givenimplementation. A plurality of struts 102 and 104 connect the first andsecond diverting rings 120, 130 to the nose cone 110. Preferably,primary struts 102 connect both the first and second diverting rings120, 130 to the nose cone 110. The secondary struts 104, preferablyoffset from the primary struts 102, connect the second diverting rings130 to the first diverting ring 120. The struts 102 and 104 arepreferably about 0.438 inches thick. Although the use of these primaryand secondary struts 120 and 130 is preferred, a person skilled in theart will appreciate that other arrangements can be used to connect therings 120 and 130 to the nose cone 110.

The flow distributor 100 is preferably symmetrical about its own centralaxis C, which is intended to substantially align with the central axis Cof the inlet section and tube sheet in which the flow distributor 100 isinstalled as described herein. Thus, the nose cone 110 and rings 120,130 are preferably symmetrical about the center axis of the flowdistributor 100, the rings 120 and 130 are preferably continuous aroundthe nose cone 110, and the struts 102 and 104 are preferablysymmetrically arranged on the flow distributor 100. In the presentembodiment of the disclosed flow distributor 100, the first ring 120 isconnected to the nose cone 110 by three primary struts 102 arrangedabout every 120-degrees. The second ring 130 is connected to the firstring 120 and the nose cone 110 by three primary struts 102 arrangedabout every 120-degrees and by three secondary struts 104 arranged aboutevery 120-degrees.

As best shown in the side view of FIG. 4B, the nose cone 110 has aleading portion 112 and a trailing portion 114 and is aerodynamicallyshaped to divert impingent gas flow around the nose cone 110. Ingeneral, the nose cone 110 is “conical” or is shaped as a “bullet,”having curvature to its outer surface. Further teachings for optimizingthe shape and size of the nose cone 110 for a given implementation areprovided below.

The first diverting ring 120 is spaced outwardly from the nose cone 110.The first diverting ring 120 has a substantially flat surface 122, aleading edge 124, and a trailing edge 126. In the present embodiment,the substantially flat surface 122 is angled at a first angle θ₁relative to the central axis C to redirect at least a portion of the gasflow diverted by the nose cone 110 into the wake or low pressure areacreated behind the nose cone 110. Further teachings for optimizing theshape and size of the first diverting ring 120 for a givenimplementation are provided below.

The second diverting ring 130 is spaced outwardly from the firstdiverting ring 120. The second diverting ring 130 has a substantiallyflat surface 132 where flow of the process gas impinges. In the presentembodiment, the substantially flat surface 132 is angled at a thirdangle θ₃ relative to the central axis C to direct gas flow both inwardlyand outwardly of the second ring 130. Further teachings for optimizingthe shape and size of the second diverting ring 130 for a givenimplementation are provided below.

Referring to FIGS. 5 through 8, components for mounting the flowdistributor 100 in an inlet section 22 of a heat exchanger arediscussed. In FIG. 5, the flow distributor 100, is shown mounted in theinlet section 22 by a plurality of mounting rods 140 and anchors 150. Arod 140 is shown in isolated detail in FIG. 7, and an anchor 150 isshown in isolated detail in FIG. 8. The rods 140 are substantiallycylindrical and have a smooth end 144 for connecting to the nose cone110, a threaded end 146 for connecting to an anchor 150, and anintermediate recess 144 for turning the rod 140 with a tool. In oneexemplary embodiment, the rods 140 have a diameter of approximately1.1-inches and have a length of about 15-inches. As shown in FIG. 5, thesmooth ends 144 of the rods 140 each position in a hole 118 transverselydefined in the nose cone 110. Preferably, the smooth ends 144 and holes118 have an amount of play accounting for thermal effects and adjustmentof tolerances. The holes 118 in the nose cone 110, which are best shownin isolated detail in FIGS. 6A-B, have a diameter of about 1.1-inchesand are positioned about 1.5-inches from the trailing end 114 of thenose cone 110.

It is preferred that the mounting rods 140 do not connect directly withthe wall 23 of the inlet section 22 because the rods 140 may conductheat from within the inlet section 22 to the wall 23. As best shown inFIG. 5, the threaded ends 146 of the rods 140 each connect to an anchor150, which are cast in the refractory 50 lining the inlet section 22.The anchors 150 each include a tubular body 152 having flared tabs 154and a threaded opening 156. The flared tabs 154 bent away from the body152 of the anchor 150 are embedded in the material of the refractory 50to help hold the anchor 150 in place. The threaded opening 156 isexposed on the surface 52 of the refractory 150 for threading with therods 140. When mounting the flow distributor 100 in the inlet section22, the threaded ends 146 of the rods 140 thread into the threadedopenings 156 of the anchors 150 exposed in the refractory 50. Theintermediate recess 148 of the rod 140 preferably receives a wrench orthe like for rotating the rod 140 when threading the end 146 into theanchor opening 156. As best shown in FIG. 8, the anchor 150 is about5-inches in length and has a diameter of about 1.5-inches. The flaredtabs 154 are about 1.9-inches long and are angled about 20-degrees fromthe body 152 of the anchor 150.

As shown in FIG. 5, it is preferred that three rods 140 and anchors 150are preferably used to mount the distributor 100 in the inlet section22. In addition, it is preferred that the rods 140 and anchors 150 aresymmetrically arranged about the central axis of the distributor 100(e.g., arranged at about every 120-degrees in the present embodiment).Moreover, it is preferred that the three rods 140 and anchors 150 areoffset by about 30-degrees from the struts 102 or 104 that interconnectthe nose cone 110 and diverter rings 120 and 130. Thus, it is preferredthat the holes 118 in the nose cone 110 are also offset by about30-degrees from the struts 102 or 104. The rods 140 are also preferablymounted forward (i.e., closer to the impingent process gas from thepipe) with respect to a center of gravity of the flow distributor 100 tocreate a caster effect on the distributor 100 and rods 140 in the flowof the process gas. When the flow distributor 100 is mounted with therods 140 in the inlet section 22, the flow of the process gas cansufficiently force the distributor 100 such that the holes 118 of thenose cone 110 are forced against the smooth ends 144 of the rods 140 toproduce a substantially rigid coupling.

Now that structural details of the disclosed flow distributor 100 havebeen discussed above, details and methods for improving the distributionof gas flow in a given implementation of an existing process heatexchanger system using the disclosed flow distributor 100 will bediscussed.

First, the gas flow characteristics of an existing process heatexchanger system are modeled using techniques of computational fluiddynamics known in the art. For example, the existing process heatexchanger system having an inlet section 22 and tube sheet 36 as shownFIG. 1 may have a number of problems associated with fouling, filmboiling, and erosion discussed in the background section of the presentdisclosure. For a given implementation, a number of variables andparameters of the system may be known or measured. For example, thedimensions and materials of the inlet section 22, the number of transfertubes 34 in the tube sheet 36, the composition of the process gas, andthe flow characteristics of the process gas may be known or measured. Acomputer model of the existing system is then created with a softwaresystem capable of performing computational fluid dynamics (CFD)analysis. Suitable CFD software systems include FIDAP by Fluent Inc. andCFX by ANSYS, Inc. As is known in the art, CFD analysis is used todevelop a 2-D, axisymmetric computational fluid dynamic model of theinlet section 22, such as schematically shown in FIGS. 1 and 2. Themodel is used to estimate the velocity profile at the face F of the tubesheet 36 under current operating conditions in the existing processsystem, such as shown in FIG. 1.

In building the computer model using CFD analysis, the known or measuredvariables and parameters of the existing process system are used incombination with a number of assumptions. Firstly, uniform flow of theprocess gas into the inlet section 22 is assumed. If non-uniform flowexists, the actual velocity at the inlet face F of the tube sheet 36 maybe higher than calculated. Secondly, the CFD model is often based on anisothermal assumption. This is acceptable because the desired analysisis on the inlet side of the tube sheet 36 and heat loss is negligible.The tube sheet 36 having the numerous tubes 34 is simulated in the CFDmodel as a porous element. The porous element properties are set so thatthe same pressure drop occurs as specified for the process gas on thetube side of the tube sheet 36.

The behavior of the process gas in the inlet section 22 at the tubesheet 36 is a complex phenomenon in which temperature, gas properties,construction material, and a number of other parameters play a role.Using such parameters, a kinetic model can be produced that describes orsimulates the behavior. For example, properties of the process gas usedin the kinetic model may include the density, viscosity, and averagevelocity of the gas. The geometry used in the kinetic model may includetube sheet pressure drop, permeability of the tube sheet governed by thenumber of tubes in the sheet, area of the tube sheet, and otherdimensions of the components. One or more of these properties anddimensions may be transformed to dimensionless parameters for use in theCFD models.

CFD analysis is then performed on the existing inlet section 22. Asnoted above in FIG. 1, the geometry of the inlet section 22 along withflow rate of the process gas can cause recirculation zones at theperiphery of the tube sheet 36, thereby increasing the peak velocity atthe tube sheet 36 and providing ideal conditions for fouling andplugging of groups of tubes 34. The existence and extent ofrecirculation zones in the inlet section 22 of the tube sheet 36 is ofparticular interest in modeling the gas flow characteristics of theexisting system. Design of the geometric shape of refractory takes intoconsideration specific gas flow characteristics, utilizing the gasproperties as well as process conditions. CFD and other analysis methodsare used to determine the appropriate geometries, pressures, and flowrates that will reduce the recirculation zones within the inlet section22. Then, changes in the geometry of the refractory and the flowdistributor 100 can then be made to optimize the reduction ofrecirculation zones in the inlet section 20 and to better distribute theprocess gas.

Based on the modeled gas flow characteristics, an optimal shape forforming the refractory 50, such as shown in FIG. 2, on the inner wall 23of the inlet section 22 is modeled to reduce the existence or extent ofrecirculation. For example, the refractory 50 can be given a trumpet orbell shaped design to eliminate recirculation zones. The refractory 50can be formed with a first tapered section that extends from the inletof the inlet cone 22, past the distributor anchors (not shown), and to apoint of about 75-80% of the axial expanse D₁ of the inlet cone 22.Then, the refractory 50 can be formed with a second tapered section toform a bell shape near the tube sheet 36. The geometric shape of therefractory 50 on the inner wall 23 of the inlet section 22 can reducethe average velocity in the inlet cone 22. If the average velocity of aninlet section without the shaped refractory 50 is about 1881 in/sec.,for example, then the shaped refractory 50 may reduce the averagevelocity to about 1590 in/sec. In addition, the geometric shape of therefractory 50 can allow the process gas to be better distributed acrossthe tube sheet 36.

Once a suitable geometry for the refractory 50 is estimated, the CFDmodel is then used to assess the inlet cone 22 having the modifiedrefractory 50 and a modeled flow distributor 100 according to teachingsof the present disclosure and as schematically shown in FIG. 2. Initialresults of axisymmetric CFD analysis are obtained with the modeled flowdistributor 100 and the modified refractory 50. Then, the modeled flowdistributor 100 and refractory 50 are co-developed in an iterativeprocess, which may require numerous iterations, to distribute theprocess gas and to allow more uniform flow distribution, velocity, andtemperature gradient on the face F of the tube sheet 36.

Exemplary details of the flow distributor 100 are discussed withreference to FIGS. 3 and 4A-B. The nose cone 110 is sized and shaped todistribute any centrally located jet of gas in the section 22 and todisperse the flow coming into the center axis C of the inlet section 22at an angle that is most conducive to redirection by the one or morerings 120, 130 of the flow distributor 100. Thus, the nose cone 110 issubstantially positioned at the central axis C of the inlet section 22and is preferably symmetric about the central axis C. A person skilledin the art will appreciate that the shape and size of the nose cone 110can vary from one implementation to another. In general, however, thebasic geometry of the nose cone 110 may not change from oneimplementation to another, but its overall size or diameter may changegiven the size of the inlet section 22, tube sheet 36, or refractory 50,for example. When performing the CFD analysis, the size of the nose cone110 may be initially selected to be about 30-40% of the inlet conediameter before the transition to the trumpet section of the modeledrefractory 50. As best shown in FIG. 4B, the nose cone 110 can generallyhave an axial expanse H₁ of about 2 to 20-inches and a radial expanse W₁of about 2 to 200-inches. The nose cone 110 preferably has a tip on theleading portion 112 that is defined by a small radius of curvature. Inaddition, the nose cone 110 preferably has an outer surface 116following the tip on the leading portion 112 that is defined by a lagerradius of curvature. The trailing portion 114 is preferably defined by asubstantially cylindrical surface.

In one exemplary implementation of FIG. 3, the piping 20 may have aradial dimension R₁ of about 11.625-inch, and the inlet section 22 tothe transfer line heat exchanger may have an axial expanse D₁ of about32-inches from the furnace piping 20 to the inlet tube sheet 36. Theinlet cone 22 may define an inside diameter at the tube sheet 36 ofabout 23-inches. The pressure drop across the tube sheet 36 may be about1.5 lb_(f)/in². The inlet flow may initially be 766,000 in³/sec, and theaverage inlet velocity may initially be about 1804 in/sec. The processgas may have a density of about 1.8×10−5 lb_(m)/in³ and a viscosity ofabout 3.9×10−9 lb_(f)/in². Once formed, the refractory 50 may have aradial dimension R₂ about 21-inches in such an exemplary implementationadjacent the tube sheet 36. Using details of the exemplaryimplementation discussed above, the axial expanse H₁ of the nose cone110 in FIG. 4B can be about 5.3-inches, and the radial expanse W₁ can beabout 3-inches, for example. In addition, the nose cone 110 for such anexemplary implementation can have a leading portion 112 defined by aradius of about 0.4-inch and can have an outer surface 116 defined byanother radius of about 9.1-inches.

The size and orientation of the one or more diverter rings 120, 130 isselected within the inlet section 22 to divert the process gas outsidethe nose cone 110. Selection of the number of rings is governed by thesize of the inlet section 22, tube sheet 36, and refractory 50 and isgoverned by the velocity and density of the process gas. In general,more than one ring may be used for lager implementations and/or forfaster and denser process gasses. In addition, a person skilled in theart will appreciate that the size of the first diverting ring 120 canvary from one implementation to another. For example, the diameter ofthe first ring 120 depends in part on the diameter of the nose cone 110.In general, the substantially flat surface 122 of the first ring 120 canbe arranged at a first angle θ₁ of about 0 to 180-degrees relative tothe central axis C to substantially redirect at least a portion of thegas flow distributed by the nose cone 110 in to the wake or low pressurearea created by the nose cone 110. The primary struts 102 connecting thefirst ring 120 to the nose cone 110 can be arranged at a second angle θ₂of about 37-degrees. The first diverting ring 120 can generally bepositioned at an axial expanse H₂ of about 3 to 300-inches so that theleading edge 124 of the first diverting ring 120 can be spaced an axialseparation S1 of about 5 to 15-inches behind the trailing portion 114 ofthe nose cone 110. The first diverting ring 120 can have a radialexpanse W₂ of about 5 to 200. The width of the first diverting ring 120can be about 0.25 to 10-inches, and the thickness can be about 0.15 to2.5-inches. Preferably, the edges of the first diverting ring 120 arerounded, as are the edges of other portions of the distributor 100.

Using the details of the exemplary implementation discussed above, thesubstantially flat surface 122 of the distributor 100 can be arranged ata first angle θ₁ of about 42-degrees relative to the central axis C toredirect at least a portion of the gas flow distributed by the nose cone110 into the wake or low pressure area of the nose cone 110. The firstdiverting ring 120 can be positioned at an axial expanse H₂ of about6.8-inches so that the leading edge 124 of the first diverting ring 120can be spaced an axial separation S1 of about 1.5-inches behind thetrailing portion 114 of the nose cone 110. The first diverting ring 120can have a radial expanse W₂ of about 5.15-inches. The width of thefirst diverting ring 120 can be about 2.0-inches, and the thickness canbe about 0.438-inches.

As noted above, an additional or second diverter ring 130 may be usedfor a given implementation. The size and orientation of the additional,second diverter ring 130 can be selected within the inlet section 22 todivert impingent gas flow. In general, the diameter of any additionalsecond ring 130 depends in part on the diameter of the first ring 120and the overall size and shape of the inlet section 22 and refractory50. To divert impingent gas flow, the substantially flat surface 132, asshown in FIG. 4B, can define an angle θ₃ of about 45 to 135-degreesrelative to the central axis C. The second diverting ring 130 can bepositioned at an axial expanse H₃ of about 2 to 100-inches and can havea radial expanse W₃ of about 5 to 500-inches. In addition, the secondring 130 can be spaced an axial separation S₂ of about 2 to 200-inchesfrom the end of the nose cone 110. The width of the second divertingring 120 can be about 0.25 to 25-inches, and the thickness can be about0.1 to 3-inches. A person skilled in the art will appreciate that thesize and orientation of the second diverting ring 130, however, can varyfrom one implementation to another.

Using the details of the exemplary implementation discussed above, thesubstantially flat surface 132 can define an angle θ₃ of about90-degrees relative to the central axis. The second diverting ring 130can be positioned at an axial expanse H₃ of about 9.0-inches and canhave a radial expanse W₃ of about 10-inches. In addition, the trailingsurface 134 of the second ring 130 can be spaced an axial separation S₂of about 4-inches from the end of the nose cone 110. The width of thesecond diverting ring 120 can be about 0.9-inches, and the thickness canbe about 0.438-inches. Therefore, as best shown in FIG. 3, the flowdistributor 100 can have an expanse D₂ of about 9-inches and may bedistanced an axial expanse D₃ from the tube sheet 36 by about 4-inchesfor such an exemplary implementation. In addition, the flow distributor100 may have an overall radial dimension R₃ of about 10-inches.

A person skilled in the art of computational fluid dynamics willappreciate that optimizing the sizes and orientations of these modeledcomponents 110, 120, and 130 of the flow distributor 100 to achieve asubstantially even distribution of process gas flow on the tube sheet 36involves an iterative process using techniques of computational fluiddynamics known in the art. It is understood that variables for aparticular implementation can vary widely from those of anotherimplementation. Guidance as to the assumptions when setting up the CFDmodel to develop the optimal geometry of the flow distributor 100 and toapproximate ranges of the positions, sizes, widths, diameters,separations, and angular orientations among the various modeledcomponents 110, 120, and 130, and so on, of the distributor 100 has beenprovided herein. During the iterative CFD analysis, it may be necessaryto first model an initial orientation and size of the refractory, nosecone, and one or more rings. After initial iterations, it may then benecessary for one to alter the shape, size, or taper of the refractoryto improve the distribution of gas. As a consequence, the orientationand size of the nose cone and one or more rings may then need to bealtered for further improvement of the results. During the iterative CFDanalysis, a number of attributes of the nose cone and one or more ringsy need to be adjusted or varied. For example, a position along a centralaxis of the input section, a diameter, an axial expanse, or a surfacecurvature of the nose cone may need to be adjusted or varied, or theradius, width, relative separation from the nose cone, or angularorientation of one or more diverter ring may need to be adjusted orvaried. Furthermore, further refinements of the refractory may berequired.

Once a preferred geometry of the components 110, 120, and 130 of theflow distributor 100 has been modeled, the inlet section 22 of theexisting process heat exchanger system is lined with the preferredgeometry of refractory 50 having embedded anchors 150, as shown in FIG.5. Then, a flow distributor 100 having the preferred modeled geometryobtained through CFD analysis is fabricated and installed in the linedinlet section 22 at the preferred position using the mounting rods 140.When so built, the disclosed flow distributor 100 redistributes the flowin the inlet section 22 so that the disclosed flow distributor 100 has alow-pressure drop and the flow is substantially equally distributedacross the face F of the tube sheet 36.

Use of the disclosed flow distributor 100 according to the teachings ofthe present disclosure in the inlet of a transfer line heat exchangercan reduce maintenance requirements of the heat exchanger and canincrease the overall heat exchange rate by about 5 to 10 percent. Forexample, the flow distributor 100 can reduce the occurrence of foulingon the tube sheet 36 and reduces damaging heat flux conditions caused byhigh flow velocities. The flow distributor 100 can improve distribution,temperature gradient, and velocity of the process gas across the tubesheet 36. The disclosed flow distributor 100 and geometry of therefractory 50 can prevent recirculation in the inlet section 22, whichreduces the potential for fouling of the tube sheet 36.

In testing, it has been shown that a flow distributor 100 according tothe teachings of the present disclosure used with preferred refractorycan reduce the peak velocity at the face F of the tube sheet 36 by asmuch as 50%. The reduction in the velocity of the process gas at theface F of the tube sheet 36 helps to lower the heat transfer filmcoefficients on the process gas side compared to that presentlyexperienced in the transfer line heat exchanger and helps to lower theassociated temperatures. In addition, the flow distributor 100 divertsparticles, if present, in the process gas from directly impacting thecenter of the tube sheet 36 and reduces the speed of any particle.

The foregoing description of preferred and other embodiments is notintended to limit or restrict the scope or applicability of theinventive concepts conceived of by the Applicants. In exchange fordisclosing the inventive concepts contained herein, the Applicantsdesire all patent rights afforded by the appended claims. Therefore, itis intended that the invention include all modifications and alterationsto the full extent that they come within the scope of the followingclaims or the equivalents thereof.

1. In a heat exchanger system having an inlet conveying gas to a heatexchanger, a device mounted in the inlet for more evenly distributingthe gas into the heat exchanger, comprising: a cone positioned in theinlet and diverting impingent gas around the cone such that an area oflow pressure is formed behind the cone; and a ring positioned outwardlyfrom the cone and redirecting at least a portion of the gas diverted bythe nose cone into the area of low pressure behind the cone.
 2. Thedevice of claim 1, wherein the cone comprises an outer surface definedby a radius of curvature.
 3. The device of claim 1, wherein the ringcomprises a substantially flat surface having gas flow impinge thereonand being oriented at an angle relative to an axial centerline of thecone that is between approximately 0 to 180-degrees.
 4. The device ofclaim 1, further comprising a plurality of struts connecting the ring tothe cone.
 5. The device of claim 1, further comprising one or moreadditional rings positioned outwardly from the ring and from each otherand diverting gas flow impingent thereon.
 6. The device of claim 5,wherein the one or more additional rings each comprise a substantiallyflat surface having gas flow impinge thereon and being oriented at anangle relative to an axial centerline of the cone that is betweenapproximately 45 to 135-degrees.
 7. The device of claim 1, furthercomprising means for mounting the device within the inlet.
 8. A devicemounting in an inlet into a heat exchanger for distributing gas,comprising: a nose cone positioned substantially on a central axis ofthe inlet and aerodynamically shaped to divert impingent gas around thenose cone; and a first diverting ring spaced outwardly from the nosecone and oriented such that at least a portion of the gas diverted bythe nose cone is redirected into the wake of the nose cone.
 9. Thedevice of claim 8, wherein the nose cone comprises an outer surfacedefined by a radius of curvature and having a leading portion with asmaller diameter than a trailing portion.
 10. The device of claim 8,wherein the first diverting ring comprises a substantially flat surfacehaving gas flow impinge thereon and being oriented at an angle relativeto an axial centerline of the nose cone.
 11. The device of claim 10,wherein the angle is between approximately 0 to 180-degrees.
 12. Thedevice of claim 8, further comprising a plurality of struts connectingthe first diverting ring to the nose cone.
 13. The device of claim 8,further comprising a second diverting ring spaced outwardly from thefirst diverting ring and oriented to divert gas flow impingent thereon.14. The device of claim 13, further comprising a plurality of strutsconnecting the second diverting ring to the first diverting ring. 15.The device of claim 13, wherein the second diverting ring comprises asubstantially flat surface having gas flow impinge thereon and beingoriented at an angle relative to an axial centerline of the cone. 16.The device of claim 15, wherein the angle is between approximately 45 to135-degrees.
 17. The device of claim 13, wherein the first divertingring is spaced a first axial distance from a trailing end of the nosecone, and wherein the second diverting ring is spaced a second axialdistance from the trailing end that is greater than the first axialdistance.
 18. The device of claim 8, further comprising a plurality ofrods for mounting the device within the inlet, each rod having a firstend connecting to the nose cone and having a second end connecting tothe inlet.
 19. The device of claim 18, wherein the nose cone definesholes receiving the first ends of the rods.
 20. The device of claim 18,further comprising a plurality of anchors mounted in refractory materiallining the inlet and having the second ends of the rods threadedtherein.
 21. A heat exchanger for gas having a tube sheet, comprising:an inlet having an inner wall and a central axis, the inlet attaching tothe heat exchanger adjacent the tube sheet; a refractory lining theinner wall of the inlet; and a device mounting in the inlet forsubstantially evenly distributing impingent gas on the tube sheet,including: a cone positioned substantially on the central axis of theinlet and diverting impingent gas around the cone; and at least one ringspaced outwardly from the cone and diverting at least a portion of thegas diverted by the cone.
 22. The device of claim 21, wherein the atleast one ring comprises a substantially flat surface having gas flowimpinge thereon and being oriented at an angle relative to an axialcenterline of the cone that is between approximately 0 to 180-degrees.23. The device of claim 21, further comprising a plurality of strutsconnecting the at least one ring to the cone.
 24. The device of claim21, further comprising a plurality of rods for mounting the devicewithin the inlet, each rod having a first end connecting to the cone andhaving a second end connecting to the inlet.
 25. The device of claim 24,further comprising a plurality of anchors fixedly mounted in therefractory and having the second ends of the rods threaded therein. 26.A method for improving an existing heat exchanger system, which includesgas conveyed to a heat exchanger through an input section, comprisingthe steps of: a) modeling the gas characteristics of the existing heatexchanger system; b) optimizing the shape of refractory in the inputsection based on the gas characteristics; c) optimizing the size andorientation of a nose cone within the input section to distribute anycentrally located jet of gas; d) optimizing the size and orientation ofone or more diverter rings within the input section to divert impingentgas within the input section; e) fabricating an assembly comprising thenose cone and the one or more diverter rings; and f) installing theassembly in the input section having the shaped refractory.
 27. Themethod of claim 26, wherein step (c) comprises the step of iterativelydetermining a position of the nose cone along a central axis of theinput section, a diameter of the nose cone, an axial expanse of the nosecone, or a surface curvature of the nose cone.
 28. The method of claim26, wherein step (d) comprises the step of iteratively determining aradius of a first diverter ring, a width of the first diverter ring, arelative separation of the first diverter ring from the nose cone, or anangular orientation of the first diverter ring to divert at least aportion of gas distributed by the nose cone into the wake of the nosecone.
 29. The method of claim 26, wherein step (d) comprises the step ofiteratively determining a radius of one or more second diverter rings, awidth of one or more second diverter rings, a relative separation of oneor more second diverter rings from the nose cone, or an angularorientation of one or more second diverter rings within the inputsection to divert gas impingent thereon.
 30. The method of claim 26,wherein step (d) comprises the step of using more than one diverter ringwithin the input section based on a size of the input section or basedon characteristics of the gas flow.
 31. The method of claim 26, whereinstep (f) comprises the step of mounting the assembly in the inletsection with a plurality of rods and anchors.